Electrodeposition of tin



Patented Oct. 5, 1948 ELECTRODEPOSITION OF TIN Elmer F. Harris, Birmingham, Ala., assignor, by mesne assignments. to Carnegie-Illinois Steel Corporation, a corporation of New Jersey No Drawing. Application October 5, 1945,

Serial No. 620,639

'7 Claims. (Cl. 204-54) This invention relates to the electrodeposition of tin, and more particularly to a novel method of electrodepositing tin and to an electrolyte by which said method may be carried out.

The invention has among its objects the provision of a novel method of electrodepositing tin, particularly as a coating on products such as strip metal, by which a dense, compact, adherent, deposit may be secured under broader ranges of current density, temperature agitation, and other bath conditions than was formerly possible.

Another object of th invention reside in the provision of an electrolyte for the eIectrodeposi-.

tion of tin which gives denser and more uniform coatings at low current densities.

These and further objects of the invention will become morefully apparent in the following description.

Broadly stated, the invention consists in the.

addition to acid or neutral electrolytes for tin plating, that is those with a pH value of 7 or less or those having a maximum upper limit in the pH value of 7, an addition agent which broadens the plating conditions, such'as temperature of the bath, degree of agitation, and current density. under which satisfactory coatings are secured. The effect of the agent added by the present invention to the plating bath is particularly noticeable in the lower current density ranges, the resuiting bath making satisfactory deposition possible at much lower current densities than formerly could be used. As a result, satisfactory coatings are secured even though plating conditions in the bath are not maintained-so accurately as was heretofore necessary.

In the electroplating of continuous strip metal, such as thin strip-steel, in connection with which the invention will be described for purposes of illustration, the strip is usually fed continuously to the electrocoating line from coils; In one such practice, the strip after being uncoiled is continuously cleaned and then coated with tin in an electrolytic bath. The coated strip is washed and dried, after which the coating is melted by running the strip through a furnace to bring the coating to a bright condition and to improve its plating bath. Such variations in speed are compensated for to some extent at least by varying the current density of the depositing current, in order to maintain a substantially uniform thickness of coating metal on the strip. when tin plating electrolytes heretofore known are employed in the coating method above described. however, it has been found that there are certain critical current densities between which the current has to be maintained to insure the deposition of a satisfactory coating. In one such prior electrolyte, the permissible plating range of current density is from 140 to 300 amperes per square foot. Current densities above and below such upper and lower limits, respectively, havebeen found to yield porous, non-uniform coatings, which, even after the melting step, were not so satisi'actory as could be desired.

In the practice of the present invention'there is added to acid or neutral tin electrodepositing electrolytes a relatively small quantity of monobutyl phenylphenol sodium monosulphonate. which has the chemical formula:

CiHo(CeHi) (CcHa) OH- SOsNa The compound ordinarily used in the present invention is the commercial product, which consists largely, of one or both of the isomers having structural chemical formulae as follows:

bond to the base metal. Such procedure is most conveniently carried out with the strip continuously in motion, the leading end of one supply coil of strip metal being Joined to the trailing end of an exhausted coil, as by being welded thereto. Such joining of coils end to end. and other conditions which may arise in the cleaning, electroplating, and melting line, cause at least an occa. sional variation in speed of the strip through the E 0 :Nii

H n butyl ctr n butyl lOlNli butyi phenylphenol sodium monosulphonate does not appear to affect the upper limit of the current density range; thus the electrolyte herein claimed has a permissible current density range of from 20 to 300 amperes per squarefoot of the material to be plated in the electrolyte.

The term monobutyl phenylphenol sodium monosulphonate as employed in this specification and the appended claims refers to commercial mixtures of isomers of the compound having the formula C4Ha(CeH4)(CeI-Is)OH'BO:Na. The quantities stated in each instance in the specification and claims are in terms of parts by weight of the pure material. As is disclosed in the copending application 620,640, filed of even date, now Patent No. 2,450,795, monobutyl phenylphenol sodium monosulphonate may also be addedto tin plating electrolytes containing small quantities of diphenyl-para-phenylene-diamine. Diphenyi-paraphenylene-diamine has been found to broaden the -permissible current density range in its upper portion. When the two such addition agents, that is, monobutyl phenylphenol sodium monosulphonate and diphenyl-para-phenylene-diamine, are employed in an electrolyte of the type disclosed they appear to have no adverse effect on each other, the resulting electrolyte being broadened in permissible current density range on both the lower and upper ends of the range.'

It has been found that the addition of monobutyl phenylphenol sodium monosulphonate within the'abov'e range broadens the lower limit'of the permissible current density range in the cases of a wide variety of acid and neutral electrolytes. As a typical example of solutions in which it has been used to advantage there is given the following:

Although electrolytes within the above ranges of components give satisfactory results, it is generally preferred to restrict the components to somewhat narrower ranges, which are given in the following Example 11:

Example I! Tin (Bn++) grams per liter 28-37 Phenol sulphonic acid (ortho, meta or para) gram per liter" 65-90 Dihydroxy diphenyl sulphone do 4-69 Monobutyl phenylphenol sodium monosuiphonate parts per million by weight 5-2000 The electrolytes disclosed in the above Examples I and II may be made by dissolving phenol sulphonic acid stannous sulphate, and dihydroxy diphenyl sulphone in water in sufficient quantities to provide a solution containing the specified amounts of free acid and dihydroxy. diphenyl sulphone. To such electrolyte is then addedfmonobntyl phenylphenol sodium monosulphonate inthe amounts specified. By the use of the above electrolytes not only is satisfactory deposition under less critical conditions of temperature and agitation possible, but as above disclosed, the current density range onthe lower side is broadstrip.

The dihydroxy diphenyl sulphone ordinarily employed is the reaction product of phenol and sulphuric acid and consists principally of 4-4- dihydroxy diphenyl sulphone and 4-2'-dihydroxy diphenyl sulphone. For convenience, this material is sometimes referred to as phenol sulphone.

Although in the electrolytes-set out in the above examples phenol sulphonic acid is employed, the addition of monobutyl phenylphenol sodium monosulphonate displays advantages when employed with neutral electrolytes and with electrolytes containing other acids singly or together. Typical of such other acids are sulphuric acid, fluosilicic acid, benzene sulphonic acid, cresolsulphonic acid, chlorobenzen sulphonic acid and nitrobenzene sulphonic acid. All of such acids readily dissolve tin from the anodes. and are cheap and easily obtainable. The sulphonic acids are particularly suitable, however, because they form extremely soluble salts of tin. When acids other than phenol sulphonic are employed, the quantities are calculated on the basis of the weight of acid molecularly equivalent to the range stated for phenol sulphonic acid.

Furthermore, although the electrolytesin the above examples contain phenol sulphone, it is to be understood that'other soluble aromatic sulphones may also be used, such as the sulphones of cresol, resorcinol, and naphthol.

As above indicated, monobutyl phenylphenol sodium monosulphonate may be employed in electrolytes containing another or other addition agents useful in broadening the upper current density range where the 'monobutyl phenylphenol sodium monosulphonate is not materially adversely efiected by the presence of such other addition agent in the electrolyte. Typical of such other addition agent for broadening the upper limit of the current density range is diphen'ylpara-phenylene-diamine. A typical electrolyte containing both monobutyl phenylphenol sodium monosulphonate and diphenyl-para-phenylene diamine is given in the following Example III:

Example If! The addition of diphenyl para phenylene diamine broadens the current density rage on the upper side to as high as 600 amperes per square foot, and thus satisfactory plating may be obtained by use of the electrolyte in Example III with a current density of from 20 to 600 amperes per square foot. Electrolytes comprising diphenyi-para-phenylene-diamine as an addition agent, and also together with monobutyl phenylphenol sodium monosulphonate as addition agents. and methods of electrodeposition with Tin grams per liter Phenol sulphonic acid do 35-110 Dihydroxy diphenyl sulphone do 1-9, Monobutyl phenylphenol sodium monosulphonate parts by million by weight 5-2000 and passing an electric current between the anode and cathode having a current density of at least 20 amperes per square foot of cathode surface in the electrolyte.

2. The method of electrodepositing tin upon a moving strip of sheet ferrousmetal which comprises providing a tin anode in an electrolyte, moving the strip progressively through the electrolyte, making the strip the cathode in the electrolyte, the electrolyte consisting of an aqueous solution of the following ingredients:

"Iin grams per liter -60 Phenol sulphonic acid do 35-110 Dihydroxy diphenyl sulphone do 1-9 Monobutyl phenylphenol sodium monosulphonate 6 ing of an aqueous solution of 10 to 60 grams per liter of tin, an acid of the group consisting o1 phenolsulphonic acid, sulphuric acid, fluosiliclc acid, benzene sulphonic acid, cresolsulphonic acid, chlorobenzene sulphonic acid, and nitrobenzene sulphonic acid, the range of acid being 35 to 110 grams per liter for phenol sulphonic acid and the molecular equivalent for the other acids, 1 to 9 grams per liter of dihydroxy diphenyl sulphone, and 5 to 2000 parts per million by weight of monobutyl phenylphenol sodium monosulphonate.

5. An electrolyte for deposition of tin consisting of an aqueous solution, having a maximum upper limit in the pH value of 7, of 10 to 60 grams l per liter of till, 1 to 9 grams per liter of a sulphone parts per million by weight; 5-2000 and passing an electric current between the anode and cathode having a current density of at least 20 amperes per square foot of strip surface in the electrolyte.

3. An electrolyte for deposition of tin consisting of an aqueous solution of 10 to 60 grams per liter of tin in the form of a soluble tin salt, 1 to 9 grams per liter of dihydroxy diphenyl sulphone, and 5 to 2000 parts per million by weight of monobutyl phenylphenol sodium monosulphonate, the solution having a maximum upper limit in the pH value of '7.

4. An electrolyte for deposition of tin consistof a substance of the group consisting of phenol;

cresol, resorcinol and naphthol, and 5 to 2000 parts per million by weight of monobutyl phenylphenol sodium monosulphonate.

6. An electrolyte for deposition of tin which consists of an aqueous solution of the following '1. An electrolyte for deposition of tin which consists of an aqueous solution of the following ingredients:

Tin grams per liter 28-37 Phenol sulphonic acid do -90 Dihydroxy diphenyl sulphone do 4-6;; Monobutyl phenylphenol sodium monosulphonate parts per million lay-weight 5-2000v ELMER F. HARRIS.

REFERENCES CITED The following references are of record in the file of this patent:

I UNITED STATES PATENTS Number Name Date 2,195,409 fFlett Apr. 2, 1940 2,271,209 Schlotter Jan. 27, 1942 2,313,371 Stack Mar. 9, 1943 

